Quantitatively mapping out the magnetic susceptibility distribution, also known as quantitative susceptibility mapping (QSM), has received increasing clinical and scientific interest in the community of magnetic resonance imaging (MRI). QSM has shown promising utilities in charactering and quantifying chemical compositions such as iron, calcium, and gadolinium, which are closely related to the diagnosis and treatment of various neurological disorders, such as Parkinson's disease, Alzheimer's disease, stroke, multiple sclerosis, and tumor. It is able to unravel novel information related to the physical property of underlying tissue because the contrast mechanism of QSM is fundamentally different from conventional MRI that is primarily based upon relaxation properties of hydrogen proton. Instead, the contrast in QSM originates from the magnetic moments of the electrons orbiting around the proton. This new kind of contrast mechanism also offers tremendous opportunity to clinicians and engineers to exploit the full utility of MRI scanners at a very low additional cost by studying the phase images generated in a MRI scan.